This invention relates generally to a shock absorber and rotary shock dampening device. More particularly, this invention relates to a device for absorbing and dampening rotary shock loading on drill bits, drill string tubulars or other component assemblies used in rotary drilling applications.
In oil drilling applications, energy from a drilling rig""s drive assembly is transferred through the drill sting to rotate the drill bit. The drill bit typically encounters many variables in formation consolidation, consistency and compressive strengths. With each change in these variables, and with inconsistencies introduced by bit wear, the resistance to penetration and resultant rotary torque requirements are in constant transition. As a result, torsional energy is either stored in, or drawn from the drill string. Since surface equipment can neither anticipate nor react to these changes, the drill string tubulars are subjected to both resonant vibration and significant random shock loading, which results in premature wear and damage to both the drill string and bit.
When the drill string and bit are experiencing high torque and high pressure, it is desirable to provide a shock absorbing coupling to eliminate rotary shock loading. Other devices have been set forth to eliminate rotary shock loading on a drilling string. However, improvements are desired.
A torsional shock absorber for dampening rotary shock loading on drill string tubulars and bits is provided. The torsional shock absorber has an outer housing that is made up of a lower splined housing and an upper housing. The lower splined housing connects to the outer piston housing and is fitted with drive splines on an inner surface. A mandrel is located within the outer housing and has drive splines on an outer surface of the mandrel that fit between the drive splines on the inner surface of the lower splined housing. The drive splines of the lower splined housing and the drive spines of the mandrel mesh so that the lower splined housing may deliver rotary energy to the mandrel. Dampening rods are positioned longitudinally between the splines of the upper housing and the splines of the mandrel to absorb shock from non-uniform torsional loading at the drive interface between the upper housing and the mandrel.
The upper housing has a cylindrical bore at its lower end for receiving a sleeve. The piston mandrel is affixed to and is part of the lower splined mandrel. The piston mandrel has an upwardly extending cylindrical section. A balancing piston is located in sealing engagement with an inner surface of the sleeve and with an outer surface of the upwardly extending cylindrical section of the piston mandrel. The balancing piston compensates for pressure variations, such as pressure increases when the drilling rig mud pumps are engaged.
A thrust bearing assembly is provided to accept axial thrust loads from the upper housing and to transfer the load to the splined mandrel. The thrust bearing assembly has an upper thrust race and a roller bearing. The upper and lower thrust races are provided with a flat surface that allows the roller bearing to slidably oscillate as torsional stress is transferred between the upper piston and the splined mandrel. A retainer cooperates with the thrust bearing to transfer tensile forces from the housing through the thrust bearing to the mandrel.